1. Technical Field
The present invention relates to a liquid crystal cell, a display device, and a method of fabricating a liquid crystal cell suitably used for injecting liquid crystal into a cell.
2. Discussion of Related Art
There has been a remarkable progress in the popularization of a liquid crystal display device used as an image display device for a personal computer, or other various monitors. The liquid crystal display device of this kind is typically constructed in a manner that a backlight as a sheet light source for illumination is provided in the backside of a liquid crystal cell and, by irradiating a liquid crystal surface having a predetermined expanse to an entirely uniform brightness, an image formed in the liquid crystal surface of the liquid crystal cell is made visible.
Such a liquid crystal cell includes signal and gate lines and the like, a thin film transistor (TFT) having an amorphous silicon layer or the like deposited thereon, a color filter, and so on, which are laminated between two glass substrates.
In fabricating the liquid crystal cell, a substrate having a TFT formed thereon and a substrate having a color filter formed thereon are opposed to each other in a separated state with a predetermined gap, and these two substrates are stuck together by a sealant coated around the opposing surfaces of the substrates. Since a so-called empty cell is formed by sticking together the two substrates in this manner, liquid crystal is injected into this empty cell.
At present, a vacuum injecting method is frequently used to inject liquid crystal into the empty cell. According to this vacuum injecting method, the empty cell is dipped in liquid crystal stored in a vessel in a chamber where a pressure is reduced to a level near a vacuum state. Then, by restoring the pressure inside the chamber to an atmospheric pressure increasedly, the liquid crystal is injected into the empty cell through an inlet formed in the empty cell.
However, even when the liquid crystal is injected by such a conventional method as described above, the injected liquid crystal may involve air to leave bubbles therein in the case where an injection condition is not proper, or there is a shortage of exhaustion or leaving time for the injection in the vacuum injecting method. This situation may cause display failures in the display region of the liquid crystal cell.
To eliminate such bubbles left behind, technologies have been already proposed, as described in the gazettes of Japanese Patent Laid-Open No. Hei 10 (1998)-186384, Japanese Patent Laid-Open No. Hei 11 (1999)-231330, and so on. According to these technologies, bubbles mixed in liquid crystal are pushed out by using a pressure roller to apply pressure to the liquid crystal cell having liquid crystal injected thereto. Even by these technologies, however, the complete removal of bubbles cannot be assured. Therefore, needless to say, there is a demand for the development of technology, which makes it possible to conduct a more efficient and sure process for removing bubbles.
In addition, when the bubbles are pushed out by applying pressure with the pressure roller, a shortage may occur in liquid crystal injected into the liquid crystal cell. However, no measures have been proposed to deal with such a case of shortage so far. This point on the shortage must be taken into consideration for actually conducting pushing-out of bubbles by applying pressure with the pressure roller.
Other problems with regard to the injection of liquid crystal into the empty cell are as follows.
That is, in the foregoing vacuum injecting method, so-called a batch process is carried out, which executes liquid crystal injection by simultaneously inserting a plurality of empty cells into the chamber. In such a batch process, a flow of process is temporarily stopped during reducing pressure (evacuation) inside the chamber and dipping in liquid crystal. Particularly, a capacity of the chamber housing the plurality of empty cells becomes inevitably increased, and it takes a long time, for example, 12 hours or more, to reduce pressure to the predetermined degree of vacuum inside the chamber. These problems interfere with an increase of production efficiency.
In addition, in the vacuum injecting method, as described above, the empty cell is dipped in the liquid crystal in the chamber set in nearly a vacuum state, and then ambient pressure inside the chamber is restored to an atmospheric pressure. Consequently, a large pressure difference occurs between the outside and the inside of the empty cell. In the case where a substrate constituting the empty cell is a plastic substrate, such a pressure difference causes substrate deformation or the like. Thus, under the present conditions, only a glass substrate can be used for the liquid crystal cell fabricated by the vacuum injecting method.
Besides the vacuum injecting method involving the foregoing problems, a so-called dropping method is presented. According to the dropping method, liquid crystal is dropped on one substrate coated with a sealant, and then this substrate is stuck with the other substrate for forming a liquid crystal cell. Even in the dropping method however, a technology must also be provided to remove bubbles efficiently and surely, and to deal with the shortage of liquid crystal during the removal of the bubbles, when the bubbles are mixed in liquid crystal.